The overall objective of the research is to complete the amino acid sequence studies in progress and to initiate new research to determine the function of serum and cell bound IgD. The following experiments will be performed to reach this objective: a. IgD Fc fragments will be isolated after brief digestion of IgD myeloma proteins with trypsin, fragmented with CNBr and the resulting fragments sequenced by automated and conventional sequencing. b. White blood cells, particularly lymphocytes, will be analyzed for presence of cell surface receptors specific for the IgD Fc fragment. Special emphasis will be placed on examining leukemic lymphocytes and lymphocytes from patients with very high IgD serum levels. c. Lymphocytes will be cultured in vitro in presence of anti-IgM or IgD and the effect on the content of ecto-5'-nucleotidase, a biochemical marker of B cell differentiation, quantitated. d. A method will be developed to study in vitro IgD synthesis by peripheral blood mononuclear cells in order to analyze the conditions and cell types involved in IgD synthesis.